1. Field of Invention
The present invention relates to a sun-tracking system and, more particularly, to a precise, compact sun-locating apparatus of a sun-tracking apparatus.
2. Related Prior Art
A concentration-type photovoltaic system operates at a higher efficiency than a conventional photovoltaic system. A concentration-type photovoltaic system must however be equipped with a sun-tracking system for efficient generation. The efficiency of the concentration-type photovoltaic system is determined by the precision of the sun-tracking system. The core of the sun-tracking system is a sun-locating apparatus.
A conventional sun-locating apparatus 6 includes a plate 61, a post 62 provided on the plate 61 and four photodiodes 63 provided on the plate 61. The photodiodes 63 are positioned to the east, west, south and north of the post 62. When sun light is cast on the sun-locating apparatus 6, the shadow of the post 62 appears on the plate 61, thus producing a potential difference between the photodiodes 63. The photodiodes 63 positioned to the east and west of the post 62 determine whether a photovoltaic system equipped with the sun-locating apparatus 6 is aligned to the sun regarding the east and west. The photodiodes 63 positioned to the south and north of the post 62 determine whether photovoltaic system is aligned to the sun regarding the south and north. If so, a photo voltaic system is rotated until the potential differences are gone, i.e., the photovoltaic system is aligned to the sun.
The sun-locating system 6 however exhibits several drawbacks. At first, the resolution or precision of the sun-locating system 6 is in proportion to the height of the post 62. Hence, it is difficult to miniaturize the sun-locating system 6.
Secondly, the precision of the sun-locating system 6 is easily affected by clouds. When the sun is shielded by a cloud, the shadow of the cloud appears on the plate 61 as well as the shadow of the post 62. Thus, the precision of the sun-locating system 6 is affected. Moreover, when the sun light is weak, the precision of the sun-locating system 6 is affected too.
Thirdly, differences between the photodiodes 63 also jeopardize the precision of the sun-locating system 6. The photodiodes 63 are supposed to be identical to one another; however, they are, in practice, different from one another regarding their photo-electric properties.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.